The present invention relates to self-supporting tubular filters and, particularly, filters useful for the filtration of blood. More particularly, this invention relates to the manufacture of such a filter having improved tear resistance when in use.
Self-supporting filter elements are known in the prior art. For example, U.S. Pat. No. 3,408,438 granted Oct. 29, 1968 to R. Staunton relates to a method of making self-supporting filter elements from fibrous materials. While the filters of Staunton can be formed into a belt or loop, they are essentially flat materials joined by a suitable fastener after a flexible support has been incorporated thereon. French Pat. No. 1,084,239 published Jan. 18, 1955 by M. Rene Jaume disclosed a method for making self-supporting tubular filters and U.S. Pat. No. 3,746,595 granted July 17, 1973 to H. Leason discloses an improvement to the filter of Jaume.
Many materials having a porosity suitable for use as a filter cannot be extruded or otherwise molded as an integral tube. Thus, as illustrated by the patents of Staunton, Jaume and Leason, such materials are formed into tubes by joining flat sheets of the material end to end upon themselves or by sealing two flat sheets to each other along their respective longitudinal edges. No matter how such a tube is formed, its longitudinal seam constitutes a line of weakness likely to rupture when exposed to substantial pressures. If such a tube is in use in a filter when its seam ruptures, it is likely that the integrity of the filter will be lost and that fluid passing therethrough will pass through the rupture in the tube without being filtered.
While such a loss of integrity is undesirable in any filtration process, its occurrence in a blood filter could be disastrous and, therefore, a highly reliable sealing of the seam is a necessity. Unfortunately, in those instances, such as blood filtration, wherein the pore size of the filter material and the material molded thereon generally prevent the formation of a mechanical lock or seal being formed between the filter material and the ribs molded to it.
Accordingly, a need exists for a tubular filter that, during its intended use, will not rupture along seam therein resulting from its formation.